light-year

noun

ˈlīt-ˌyir 

1

: a unit of length in astronomy equal to the distance that light travels in one year in a vacuum or about 5.88 trillion miles (9.46 trillion kilometers)

2

: an extremely large measure of comparison (as of distance, time, or quality)

seems like light-years ago

has light-years more talent

two minutes and yet light-years away from the crowded village

—Suzanne Patterson

Synonyms of light-year

• world
• galaxy

Examples of light-year in a Sentence

my sister and I are close in age, but personality-wise, there are light-years between us

Recent Examples on the Web

Your rocket ship will have already traveled more than 10 light-years (but less than 15), but someone back on Earth will have experienced more than 20 years of time passing. —Big Think, 12 Mar. 2026

The merger occurred around 910 million light-years away, resulting in the creation of a daughter black hole with around 13 times the mass of the sun. —Robert Lea, Space.com, 11 Mar. 2026

Sprawling galaxies and cosmic structures that expand for light-years have often been the focus of the observatory’s infrared gaze, but so have distant, faint objects. —Ashley Strickland, CNN Money, 10 Mar. 2026

Stars are gigantic fusion reactors light-years away that do not shape our personalities or life events. —Manon Bischoff, Scientific American, 8 Mar. 2026

Word History

First Known Use

1864, in the meaning defined at sense 1

Rhymes for light-year

• atmosphere
• biosphere
• centromere
• chemosphere
• chromosphere
• hemisphere
• hydrosphere
• lithosphere
• mesosphere
• microsphere
• miserere
• mountaineer

Kids Definition

light-year

noun

ˈlīt-ˌyi(ə)r

1

: a unit of length in astronomy equal to the distance that light travels in one year or 5,880,000,000,000 miles (9,460,000,000,000 kilometers)

2

: a very great distance especially in progress

light-years ahead in design